This invention relates to a tripod type constant-velocity universal joint in which torque is transmitted between an outer ring, having three track grooves formed in the inner periphery thereof, and a tripod member mounted therein so as to be axially movable.
A tripod type constant-velocity universal joint is known which comprises an outer ring formed with three axially extending track grooves in its inner periphery, a tripod member mounted in the outer ring and having three trunnions formed thereon, cylindrical roller guide surfaces formed in side faces of each track groove so as to oppose each other in the circumferential direction of the outer ring, raceway grooves extending in the axial direction of the outer ring, and a spherical roller supported on each trunnion so as to be pivotable relative to the trunnion and received in the each track groove for transmitting a torque between the outer ring and the tripod member.
With this tripod type constant-velocity universal joint, when torque is transmitted with the tripod member taking a working angle relative to the outer ring, the center of rotation of the spherical roller is inclined relative to the lengthwise direction of its corresponding track groove. Thus, the spherical roller cannot make a pure rolling movement, so that slip occurs between the spherical roller and the roller guide surface in the track groove.
This increases the frictional resistance at a contact point between the spherical roller and the roller guide surfaces, and increases slide resistance when the outer ring and the tripod member move axially relative to each other. Therefore, vibration and noise are produced and the NVH ( noise, vibration and harshness) properties worsen.
A tripod type constant-velocity universal joint of this type is proposed in JP patent publication 64-5164 to improve NVH properties. In this type of universal joint, three track grooves are formed in the inner periphery of the outer ring and raceway grooves extending in the axial direction of the outer ring are formed in both sides of each track groove, which raceway grooves oppose each other in a circumferential direction of the outer ring. Three trunnions are formed on the tripod member which is mounted in the outer ring. A guide block supported on each trunnion so as to be pivotable relative to the trunnion is received in a corresponding track groove. Balls are mounted between raceway grooves formed on both sides of each guide block and the raceway grooves formed in the outer ring to transmit torque between the outer ring and the tripod member through the balls.
In this tripod type constant-velocity universal joint, since the balls are mounted between the raceway grooves of the outer ring and the raceway grooves of the guide blocks, when torque is transmitted with the outer ring and the tripod member forming a working angle, the guide blocks move in an axial direction of the outer ring with their attitude kept constant. Since the balls always roll in contact with the raceway grooves as the tripod member moves relative to the outer ring, vibration and noise are extremely low, so that the NVH properties are good.
In the tripod type constant-velocity universal joint shown in the above said publication, portions for preventing the balls from falling off have to be provided at both ends of each raceway groove of the guide blocks. Thus, when the working angle between the outer ring and the tripod member is large, the balls cannot roll smoothly and slip occurs because the balls contact these fall-preventive portions, so that in a slip region, the NVH properties worsen.
In order to avoid this problem, in the constant-velocity universal joint described in JP patent publication 4-74565, a plurality of balls mounted between the raceway grooves of the guide blocks and the raceway grooves at both sides of the track grooves of the outer ring are retained by a retainer and the moving distance of movement of the retainer is restricted to half of the moving distance of the guide blocks by a moving distance restricting means so that the balls can always do a pure rolling motion.
With a conventional tripod type constant-velocity universal joint, it was sometimes impossible to cause a plurality of rolling elements to make a pure rolling movement over the entire moving range of the guide block when there is certain relationship between the required moving distance of the guide block, the number of the rolling members, the pitch between the rolling members, a length of the guide block and a length of the track groove of the outer ring.
The first object of the present invention is to provide a tripod type constant-velocity universal joint which has good NVH properties.
With this already proposed tripod type constant-velocity universal joint, since the tripod member is movable in the axial direction of the outer ring, during transportation or while mounting on an automobile, the tripod member may come off the outer ring. If the tripod member comes off, the rolling elements would fall off the retainer. Moreover, since the open end of the outer ring is closed by a boot, it is impossible to reassemble parts such as the tripod member.
The second object of this invention is to prevent the tripod member from falling in such a tripod type constant-velocity universal joint.